308 or RHS on a 408

308s are an LA head with "high swirl" intake ports and a magnum-esque exh port. They are no more prone to cracking than any other LA based head. I've seen more cracked X/J/915 heads than 308s. I've never seen a cracked 308 come to think of it. That's owning or using around 10 pairs. Magnum heads will almost always show cracks, some are not an issue other than visual/emotional, but most factory Magnums show cracks. The last set of 308s done properly and with good parts (albeit in CT...lol) were $1100. That includes milling the decks and intake side for the intake fit.